In-situ interlocking of metals using additive friction stir processing

ABSTRACT

A method for joining materials using additive friction stir techniques is provided. The method joins a material to a substrate, especially where the material to be joined and the substrate are dissimilar metals. One such method comprises (a) providing a substrate with one or more grooves; (b) rotating and translating an additive friction-stir tool relative to the substrate; (c) feeding a filler material through the additive friction-stir tool; and (d) depositing the filler material into the one or more grooves of the substrate. Translation and rotation of the tool causes heating and plastic deformation of the filler material, which flows into the grooves of the substrate resulting in an interlocking bond between the substrate and filler material. In embodiments, the depositing of the filler material causes deformation of the grooves in the substrate and an interlocking configuration between the grooves of the substrate and the filler material results.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. patent application Ser.No. 14/643,396 filed Mar. 10, 2015, which published as U.S. PatentApplication Publication No. 20160175982 on Jun. 23, 2016. The '396application is a Continuation-in-Part (CIP) of U.S. patent applicationSer. No. 14/573,430 filed Dec. 17, 2014, which issued as U.S. Pat. No.9,266,191 on Feb. 23, 2016. The disclosures of these applications areincorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is in the field of solid state materials joining.In particular the invention is in the field of joining, coating, orcladding of metals, such as two dissimilar or incompatible materialsthat are not typically recommended for conventional coating or claddingor joining.

Description of Related Art

Friction-stir processing provides for the solid state joining of piecesof metal at a joint region through the generation of frictional heat atthe joint and opposed portions of the metal pieces by cyclical movementsof a tool piece that is harder than the metal pieces. An example of thisis provided by International Application Publication No.PCT/GB1992/002203. Frictional heat produced between the substrate andthe tool during the process causes the opposed portions of the substrateto soften, and mechanical intermixing and pressure cause the twomaterials to join. Typically, two materials are placed side-by-side andare joined together at the seam between the two.

Additive friction-stir fabrication, invented by the present inventors(see U.S. Pat. Nos. 8,636,194; 8,632,850; 8,875,976; and 8,397,974, thecontents of which are hereby incorporated by reference in theirentireties), is an additive process for joining materials. Additivefriction-stir fabrication (FSF) processes use shear-induced interfacialheating and plastic deformation to deposit metallic coatings onto metalsubstrates. FSF coatings have bond strengths superior to those ofthermally sprayed coatings, and have the potential to enhance corrosionresistance, enhance wear resistance, repair damaged or worn surfaces,and act as an interfacial layer for bonding metal matrix composites. Inthis process, the coating material, such as a metal alloy, is fedthrough a rotating spindle or tool to the substrate surface. As shown inFIG. 1, frictional heating occurs at the filler/substrate interface dueto the rotational motion of the filler material, such as a rod 23, at anangular velocity w and the downward pressure P applied. The mechanicalshearing that occurs at the interface acts to disperse any oxides orboundary layers, resulting in a metallurgical bond between the substrate10 and filler material/coating 25. As the substrate 10 moves relative tothe tool 15, the coating is extruded under the rotating shoulder of thestirring tool 15.

Conventional techniques are incapable of bonding dissimilar materialssuch as steel and aluminum. Currently, explosive bonding is used toachieve solid state cladding of dissimilar materials. Explosive bondinguses controlled detonations to accelerate one metal plate into anothercreating an atomic bond. This method has numerous limitations related tomaterial pairing, thickness and the environment in which it isconducted. Additional techniques include those described by Geiger M. etal, Friction Stir Knead Welding of steel aluminum butt joints,International Journal of Machine Tools & Manufacture 48 (2008) 515-521),and those described in U.S. Patent Application Publication No.20120273113, U.S. Pat. No. 4,023,613, and Chinese Patent No. CN102120287 B. Despite these efforts, however, there remains a need in theart for new techniques for joining dissimilar materials.

SUMMARY OF THE INVENTION

The present invention is a method for joining materials using additivefriction stir techniques. The method can be used to join a material to asubstrate, especially where the material to be joined and the substratecomprise dissimilar metals.

One such method comprises (a) providing a substrate with one or moregrooves; (b) rotating and translating an additive friction-stir toolrelative to the substrate; (c) feeding a filler material through theadditive friction-stir tool; and (d) depositing the filler material intothe one or more grooves of the substrate. In preferred embodiments,substrate(s) with multiple grooves are provided. Translation androtation of the tool causes heating and plastic deformation of thefiller material, which flows into the grooves of the substrate resultingin an interlocking bond between the substrate and filler material. Inembodiments, the depositing of the filler material causes deformation ofthe grooves in the substrate and an interlocking configuration betweenthe grooves of the substrate and the filler material results.

The grooves of the substrate can have an opening, a base, and parallelsidewalls extending from the opening to the base. In embodiments, thegrooves have an opening, a base, and perpendicular sidewalls extendingfrom the opening to the base thereby providing the groove with a squareor rectangular shaped cross section. In other embodiments, the grooveshave an opening, a base, and parallel sidewalls sloping from the openingto the base. Additionally or alternatively, the grooves can have anopening, a base, and sidewalls sloping in opposite directions from theopening to the base. The opening of the groove can have a width largerthan a width of the base. The opening can alternatively have a widthsmaller than a width of the base, thereby providing the groove with adovetail shaped cross section.

According to embodiments, the methods can comprise deforming the openingto the groove thereby providing a mechanical lock between the fillermaterial and the groove. The deforming can be performed during thedepositing of the filler material into the grooves of the firstsubstrate.

In preferred embodiments, the first substrate and the filler materialcan each be metal. For example, the first substrate and the fillermaterial can each be metal independently chosen from steel, Al, Ni, Cr,Cu, Co, Au, Ag, Mg, Cd, Pb, Pt, Ti, Zn, Fe, Nb, Ta, Mo, W, or an alloycomprising one or more of these metals. In particular embodiments, thefirst substrate comprises steel and the filler material is metal chosenfrom steel, Al, Ni, Cr, Cu, Co, Au, Ag, Mg, Cd, Pb, Pt, Ti, Zn, Fe, Nb,Ta, Mo, W, or an alloy comprising one or more of these metals. Thefiller material can be a powder, pellet, rod, or powdered-filledcylinder.

Another method includes providing a sheet of metal or a metal plate as asecond substrate and deforming and depositing the sheet of metal or themetal plate into the one or more grooves of the substrate.

Articles of manufacture are also included within the scope of theinvention. For example, included is an article of manufacturecomprising: two different metals disposed in an interlockingconfiguration; and a joint between the two metals along an area ofinterlocking; wherein a cross section of the joint reveals each of thetwo metals having a portion providing two-dimensional projections intothe area of interlocking; and wherein the two-dimensional projectionsare of concave polygon shaped.

Methods for coating, cladding, or joining two dissimilar materials areparticular features of the invention. In one embodiment, the methodcomprises providing a first substrate and a second substrate, whereinthe first substrate has grooves disposed on a surface of the firstsubstrate. The method further comprises overlaying the first substratewith the second substrate and moving a rotating additive friction-stirtool along the second substrate over the grooves so that it heats thesecond substrate. A consumable portion of the additive friction stirtool combines with the second substrate and they are plasticizedtogether so that the plasticized material flows into the grooves,allowing the first material to be bonded to the second material throughan interlocking connection. In yet another embodiment, the methodcomprises provided a substrate with grooves disposed on the surface ofthe substrate. The method further comprises moving a rotating additivefriction stir tool along the grooves. A consumable material from therotating additive friction stir tool flows into the grooves, whilefriction from the rotating additive friction stir tool deforms thegrooves and locks the deposited material into the grooves.

The methods of the invention are useful for creating a variety ofcomposite materials with layers of dissimilar composition andproperties. Practical applications of these composite materials includeuse as components for manufacturing automobiles, ships, tanks, planes,and aerospace vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate certain aspects of embodiments ofthe present invention, and should not be used to limit the invention.Together with the written description the drawings serve to explaincertain principles of the invention.

FIG. 1 is a schematic diagram showing an additive friction stir process.

FIG. 2 is a schematic diagram showing mechanical interlocking methodembodiments using additive friction stir.

FIG. 3 is a schematic diagram showing a continuous feeding system foruse in the invention.

FIG. 4 is a macrograph image showing a cross section of an article ofmanufacture comprising two different metals (molybdenum and copper) inan interlocking configuration prepared according to an embodiment of theinvention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to various exemplary embodiments ofthe invention. It is to be understood that the following discussion ofexemplary embodiments is not intended as a limitation on the invention.Rather, the following discussion is provided to give the reader a moredetailed understanding of certain aspects and features of the invention.

FIG. 2 shows a general process 5 of material coating, cladding, orjoining through mechanical interlocking. The process preferablycomprises the coating, cladding, or joining of materials, such asdissimilar materials for example two different metals. The generalprocess involves coating, cladding, or joining a material to a firstsubstrate 10 having a grooved surface 30. Any number of grooves or typeof groove pattern can be used. In preferred embodiments, multiplegrooves are present in the substrate, such as from 1-100 grooves, orfrom 5-50 grooves, or from 10-40 grooves, or from 20-30 grooves, such as2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19grooves are present in the substrate. The number of grooves may bedependent on the particular application and/or size of substrate beingused. Methods of creating the grooves in the substrates can includelaser machining, friction based machining, conventional machining,and/or metal forming on the surface or the edges of the substrate toname a few.

One embodiment of the method is designed to join a coating of dissimilarmaterial to a substrate. As shown in FIG. 2, the friction stir tool 15is passed directly over the first substrate 10 over the grooved surface30. In this embodiment, the grooves may include dove-tail shaped grooves31, but preferably square-shaped grooves 33. The rotating friction-stirtool 15, typically non-consumable (or harder than the substrate andfiller materials), is fed with a consumable filler material 23 (such asa powder or rod) such that the consumable filler material 23 isdeposited into the grooves 33 while friction produced by thefriction-stir tool 15 generates plastic deformation of the grooves tointerlock the deposited material into the grooves 33. Thus, additivefriction stir tool 15 will touch the grooved surface 33 to deform thegrooves 33 and lock the deposited metal into the grooves 33.

Another embodiment of the invention comprises an additive friction stirmethod comprising providing a substrate having a grooved surface,translating a rotating additive friction-stir tool along the surface ofthe substrate along a vector that overlies one or more of the grooves ofthe grooved surface, and feeding the rotating friction-stir tool with afiller material (e.g., consumable filler material) such that the fillermaterial is deposited into the grooves while friction produced by thefriction-stir tool generates plastic deformation of the grooves tooverlap a portion of the deposited filler material disposed within thegrooves, thereby interlocking the substrate and filler.

Articles of manufacture can be prepared by such processes and caninclude articles of manufacture comprising metals (preferably twodifferent metals) disposed in an interlocking configuration with a jointbetween the two metals along an area of interlocking; wherein a crosssection of the joint reveals each of the two metals having a portionproviding two-dimensional projections into the area of interlocking; andwherein the two-dimensional projections are of concave polygon shape.For example, shown in FIG. 2 are cross-sectional views of the joints(with grooves 31, 33) of each of two embodiments of articles ofmanufacture that can be prepared according to the invention. Asillustrated, the metals on both sides of the joint with grooves 31 eachhave two-dimensional projections into the area of interlocking that areof a convex polygon shape, and are the same shape. In contrast, themetals of the joint with grooves 33 on either side of the joint havetwo-dimensional projections into the area of interlocking that are aconcave polygon shape. Additionally, the two-dimensional projection onone side of the joint with grooves 33 is the same shape as thetwo-dimensional projection on the other side of the joint. Thetwo-dimensional projections on either side of the joint can be the sameor different shapes and all on one side can be the same or differentshapes.

In another embodiment, a pre-fabricated layer (such as a sheet or plate)of material can be joined to a substrate. The substrate comprises agrooved surface and can include grooves that are interlocking in shapesuch as dovetail grooves 31. The grooves can have an opening, a base,and sidewalls sloping in opposite directions from the opening to thebase. The opening of the grooves can have a width smaller than a widthof the base of the grooves, or the opening of the grooves can have awidth larger than a width of the base. In one embodiment, the groovesare provided with a dovetail shaped cross section when the grooves havea width smaller than a width of the base and when the sidewalls are alsosloping in opposite directions from the opening to the base. In otherembodiments, the grooves of the substrate can have an opening, a base,and parallel sidewalls extending from the opening to the base. In suchembodiments, the grooves can have a square or rectangular shaped crosssection.

In methods where a sheet of metal or a metal plate is used, a secondsubstrate 20 is disposed on the first substrate 10 over the grooves 30of the grooved surface of the first substrate. Further, in embodiments,there is no depression or groove(s) on the surface of the secondsubstrate. An additive friction-stir tool 15 is passed over the secondsubstrate 20 along a vector overlying one or more of the grooves 30. Thefriction-stir tool 15 rotates and during rotation a filler material 23(such as a powder or rod) is fed through the friction-stir tool 15.Interaction of the rotating non-consumable friction-stir tool 15 withthe second substrate 20 generates plastic deformation at an interfacebetween the rotating non-consumable friction-stir tool 15 and the secondsubstrate 20 such that the consumable filler 23 and the second substrate20 are extruded into one or more of the grooves 30 of the firstsubstrate 10 to interlock the second substrate 20 with the firstsubstrate 10. Thus, deposition can be performed with or without touchingthe additive friction stir tool 15 to the grooves 30 on the surface ofthe first substrate 10. In this case, a dovetail type groove 31 patternwill be most beneficial for achieving improved joint properties.

Thus, one embodiment of the invention provides an additive friction stirmethod comprising providing a first substrate having a grooved surface,providing a second substrate having a composition that is different thanthe first substrate, overlaying the second substrate over the firstsubstrate such that a surface of the second substrate is incommunication with the grooved surface, translating a rotatingnon-consumable friction-stir tool along an opposing surface of thesecond substrate along a vector that overlies one or more grooves of thegrooved surface and feeding the rotating non-consumable friction-stirtool with a consumable filler material such that interaction of therotating non-consumable friction-stir tool with the second substrategenerates plastic deformation at an interface between the rotatingnon-consumable friction-stir tool and the second substrate such that theconsumable filler and second substrate are extruded through the one ormore of the grooves of the first substrate to interlock the secondsubstrate with the first substrate in situ.

In this embodiment, during translating the rotating non-consumablefriction stir tool does not penetrate the second substrate, so that nodepression is formed on the surface of the second substrate. Thus, thenon-consumable portion of the tool may generate friction at the surfaceof the second substrate without substantial penetration into the secondsubstrate. Not wishing to be bound by theory, this may be due to theaddition of consumable filler material being added during the processwhere a volume of filler material is provided underneath thenon-consumable portion of the tool.

The steps of the methods may be repeated to add successive layers ofmaterials. For example, upon joining of a first substrate with a secondsubstrate, the surface of the second substrate may be machined to form agrooved surface. Then a third layer may be added using the first orsecond embodiment of the method, and so on. Possibilities include themanufacture of bimetallic composites with alternating layers ormulti-metallic composites with completely different layers. Compositeswith three, four, five, six, seven, eight, nine, ten or more layers areeven possible.

Methods of the invention may include combinations of the features of theembodiments described above. Some embodiments may need machining ofdovetail grooves 31, and other embodiments may only need simplesquare-shaped grooves 33, which are economical in terms of machining.However, other embodiments may include some combination of dovetailgrooves 31 and square-shaped grooves 33. Additionally, a method of theinvention may include (1) providing a first substrate with a groovedsurface (2) overlaying a portion of the first substrate with a secondsubstrate, leaving some portions of the first substrate exposed (3)translating an additive friction stir tool over the second substrate ina vector overlying the grooves (4) translating an additive friction stirtool directly over the first substrate at the exposed portions (5)optionally, repeating steps 1-4. Alternatively, the second substrate mayinclude multiple panels of different thicknesses or material types. Inthis way, it is possible to introduce features into the surfacegeometries of the joined materials.

The joint strength of the samples produced in these methods will dependon the geometry of the groove pattern and the surface characteristics ofthe grooved surfaces. Finite element analysis can be conducted topredict the optimal grove geometry and surface characteristics. Desiredgroove pattern and surface characteristics can be achieved usingdifferent manufacturing processes such as various machining techniques,etching, milling, and/or plating. In one embodiment, grooves aremachined on a surface of the first substrate through a ComputerNumerical Control (CNC) machine. The grove patterns may be programmed inComputer-Aided Design (CAD) programs. The grooves may be of any uniformgeometric shape, including polygonal shapes (e.g. square, rectangular,triangular, trapezoidal), complex polygon shapes (e.g. combinations oftwo or more polygonal shapes, or convex or concave polygon shapes), ornonpolygonal shape (e.g. semi-circular, semi-oval). Further, the groovepattern may include multiple grooves representing different shapes. Thedensity of the groove pattern will depend on the size of the grooves,with smaller grooves being provided at a higher density on the surfacethan larger grooves. The size of the grooves depends on the particularapplication and the size of the additive friction stir tool used. Forexample, for certain substrates, the depth of the grooves from theopening to the base of the groove (measured perpendicularly from theopening to the base) may range anywhere from 10 micrometers to 10 mm indepth or width, or any range in between, including 10 micrometers to 1mm, and 1 mm to 10 mm. Thicker materials are capable of even deepergrooves for bonding, including those exceeding 10 mm, such as 1 cm, 10cm, or between 10-100 cm or more. The grooves may be provided at uniformor varying depth. General dimensions may range from shallow and wide todeep and narrow or anywhere in between. The optimal size and shape ofthe grooves may be achievable through routine experimentation. Thegrooves may be present on the first substrate in any pattern, includinglinear and non-linear. After obtaining the desired groove pattern andsurface characteristics, additive friction stir can be used to interlockthe filler material and/or second substrate to the first substrate usingany of the methods described in this specification.

Various combinations of materials may serve as the filler material, orthe first and second substrate. Suitable materials include a differencein melting temperature, density, and/or hardness of up to about 50%,such as from 2-20%, including at least about 10%. In one embodiment,materials that have a higher melting temperature or that are denser orharder serve as the first substrate, and materials that have a lowermelting temperature or are less dense or lighter serve as the fillermaterial and/or second substrate.

Materials that may serve as the filler material or as the first andsecond substrate may include metals and metallic materials, polymers andpolymeric materials, ceramics and ceramic materials, as well ascombinations of these materials. Metal matrix and polymer matrixcomposites, as well as metal to polymer joints are also included withinthe scope of the invention. The filler material, and the first andsecond substrate may include without limitation metal-metalcombinations, polymer-polymer combinations, metal-polymer combinations,metal-ceramic combinations, and polymer-ceramic combinations. Thematerial of the first substrate should have a machinable surface forforming the described grooves. In one particular embodiment, the firstand second substrates and/or the filler material are metal or metallic.The filer material, or the first substrate and second substrate may beindependently selected from any metal, including for example steel, Al,Ni, Cr, Cu, Co, Au, Ag, Mg, Cd, Pb, Pt, Ti, Zn, Fe, Nb, Ta, Mo, W, or analloy comprising one or more of these metals. In embodiments, the firstsubstrate and second substrate may be provided as sheet metal ormetallic plates in a variety of dimensions for joining, including with awidth and/or length of from about 1 inch to about 20 feet, such as forexample 2′×2′, 2′×3′, 2′×4′, 3′×4′, 4′×4, 5′×5, 6′×4′, and the like. Thesize of the sheets is highly dependent on and can fit any desiredapplication. Depths of the substrates as described above may be on theorder of micrometers to centimeters.

In one embodiment, the first substrate has a density in the range of7.75-8.10 g/cm³, a thermal expansion of 9.0-20.7 10⁻⁶/k, a melting pointin the range of 1371-1454° C., a tensile strength of 515-827 MPa, and ahardness of 137-595 Brinell, and the filler material and/or secondsubstrate has a density in the range of 2.50-3.00 g/cm³, a thermalexpansion in the range of 20.4-25.0 10⁻⁶/k, a melting point in the rangeof 600-700° C., a tensile strength of 310-350 MPa, and a hardness ofabout 85-95 Brinell. However, these values are merely illustrative andexemplary. A skilled artisan can identify materials with desiredproperties for particular applications.

In these additive friction stir process embodiments, the filler material(for example, solid bar or powder) can be fed through the rotatingadditive friction stir tool where frictional and adiabatic heatingoccurs at the filler/substrate interface due to the rotational motion ofthe filler and the downward force applied. The frictional and adiabaticheating that occurs at the interface results in a severe plasticdeformation at the tool-metal interface. In embodiments, as the frictionstir tool moves along the along a vector overlying the grooves (or withany relative motion between the substrate and tool), the plasticizedmetal from the filler material and/or second substrate can be extrudedunder the rotating shoulder of the tool into the grooves of the firstsubstrate. In embodiments, the rotating additive friction stir tool cancontact the grooved surface of the first substrate directly to depositthe filler/substrate into the groove directly and deform the groove,thereby locking the deposited material into the grooves.

The filler material may be of a similar or dissimilar material as thatof the first substrate and/or second substrate materials. In aparticular embodiment, the filler material is a metallic material.Non-limiting examples of metallic materials useful as a filler materialinclude steel, Al, Ni, Cr, Cu, Co, Au, Ag, Mg, Cd, Pb, Pt, Ti, Zn, Fe,Nb, Ta, Mo, W, as well as alloys of two or more of these metals and thelike. In another embodiment, the filler material is a polymericmaterial. Non-limiting examples of polymeric materials useful as afiller material include polyolefins, polyesters, nylons, vinyls,polyvinyls, acrylics, polyacrylics, polycarbonates, polystyrenes,polyurethanes, and the like. In still yet another embodiment, the fillermaterial is a composite material comprising at least one metallicmaterial and at least one polymeric material. In other embodiments,multiple material combinations may be used for producing a composite atthe interface.

In one embodiment, the filler material is the same as the secondsubstrate. The filler material may be deposited on top of a sheetmaterial comprising the second substrate as in the first embodiment ormay be deposited directly from the tool on top of the first substrate asin the second embodiment.

The filler materials can be in several forms, including but not limitedto: 1) metal powder or rod of a single composition; 2) matrix metal andreinforcement powders can be mixed and used as feed material; or 3) asolid rod of matrix can be bored (e.g., to create a tube or other hollowcylinder type structure) and filled with reinforcement powder, ormixtures of metal matric composite and reinforcement material. In thelatter, mixing of the matrix and reinforcement can occur further duringthe fabrication process. In embodiments, the filler material may be asolid metal rod. In one embodiment, the filler material is aluminum.

In embodiments, the filler material is joined with a substrate usingfrictional heating and compressive loading of the filler materialagainst the substrate and a translation of the rotating friction tool.The filler material may be a consumable material, meaning as frictionalheating and compressive loading are applied during the process, thefiller material is consumed from its original form and is applied to thesubstrate. Such consumable materials can be in any form includingpowders, pellets, rods, and powdered-filled cylinders, to name a few. Asthe applied load is increased, the filler material and substrate at thetool-substrate interface become malleable as a result of frictional andadiabatic heating and are caused to bond together under the compressiveload. In a first embodiment, the deformed metal is then extruded intothe grooves of the first substrate below the second substrate. In asecond embodiment, the tool touches the groove pattern directly anddeposits the filler material into the grooves.

The rotating additive friction stir tool may take a variety of forms.For example, the tool can be configured as described in any of U.S.Published Application Nos. 2008/0041921, 2010/0285207, 2012/0009339, and2012/0279441, 2012/0279442, as well as International Patent ApplicationPublication No. WO2013/002869. Friction-based fabrication tooling forperforming methods of the invention are preferably designed orconfigured to allow for a filler material to be fed through or otherwisedisposed through an internal portion of a non-consumable member, whichmay be referred to as a throat, neck, center, interior, or through holedisposed through opposing ends of the tool. This region of the tool canbe configured with a non-circular through-hole shape. Various interiorgeometries for the tooling are possible. With a non-circular geometry,the filler material is compelled or caused to rotate at the same angularvelocity as the non-consumable portion of the tool due to normal forcesbeing exerted by the tool at the surface of the tool throat against thefeedstock. Such geometries may include a square through-hole and anelliptical through-hole as examples. In configurations where onlytangential forces can be expected to be exerted on the surface of thefiller material by the internal surface of the throat of the tool, thefeed stock will not be caused to rotate at the same angular velocity asthe tool. Such an embodiment may include a circular geometry for thecross-section of the tool in combination with detached or looselyattached feedstock, which would be expected to result in the fillermaterial and tool rotating at different velocities. As used in thisdisclosure, the terms “additive friction-stir tool”, “friction-stirtool”, “non-consumable friction-stir tool”, and “rotating non-consumablefriction-stir tool” may be used interchangeably.

In embodiments the throat of the tool may be shaped with a non-circularcross-sectional shape. Further desired are tooling wherein the throat ofthe tool is shaped to exert normal forces on a solid, powder, orpowder-filled tube type filler material disposed therein. Embodimentsmay also include features to ensure the frictional heating andcompressive loading are of a degree sufficient to enable mixing ofdispensed filler material with material of the substrate at afiller-substrate interface.

More specifically, the magnitude of force transferred from the rotatingtool to the filler material is dependent on the coefficient of frictionbetween the two. Thus, if the coefficient of friction is significantlylow and the inertial force required to induce rotation of the fillermaterial is significantly high, then the tool can rotate withoutinducing rotation (or with inducing rotation at a lower speed than thetool) in the cylindrical filler material. Under some circumstancesduring operation, differences in rotational velocity between the tooland the filler within the tool can lead to some filler material beingdeposited inside the tool, an accumulation of which can be problematic.Having the specific interior tool geometries described in thisdisclosure can reduce this issue, such as appropriately sizedsquare-square or elliptical-elliptical shaped filler-dispensergeometries. Another way of reducing the difference in rotationalvelocity between the tool and the filler material is to manufacturefiller material rods to fit tightly within the throat of the tool, or tootherwise tightly pack the filler material into the throat of the tool.

Any shape of the cross section of the interior of the tool that iscapable of exerting normal forces on a filler material within the toolcan be used. The throat surface geometry and the filler materialgeometry can be configured to provide for engagement and disengagementof the tool and filler material, interlocking of the tool and feedmaterial, attachment of the tool and feed material, whether temporary orpermanent, or any configuration that allows for the filler material todependently rotate with the tool.

The interior surface shape of the tool (the throat) and thecorresponding shape of the filler material may not be critical and canbe constructed in a manner suitable for a particular application. Shapesof these surfaces can include, but are by no means limited to, square,rectangular, elliptical, oval, triangular, or typically any non-circularpolygon. Additional shapes may include more distinctive shapes such as astar, daisy, key and key-hole, diamond, to name a few. Indeed, the shapeof the outside surface of the filler material need not be the same typeof shape as the surface of the throat of the tool. For example, theremay be advantages from having a filler material rod with a squarecross-section for insertion into a tool throat having a rectangularcross-section, or vice-versa where a filler material rod having arectangular cross-section could be placed within a tool throat having asquare cross-section in which the corners of the filler material rodcould contact the sides of the square throat instead of sides contactingsides. Particular applications may call for more or less forces to beexerted on the filler material within the throat during operation of thetool. With concentric shapes and very close tolerance between the fillermaterial and the tool certain advantages may be realized. Additionally,different shapes may be more suitable for different applications or maybe highly desired due to their ease of manufacturing both the interiorof the tool and corresponding filler material rods. One of ordinaryskill in the art, with the benefit of this disclosure, would know theappropriate shapes to use for a particular application.

Additional embodiments of additive friction stir tools according to theinvention include a tool with one or more pins or projections. The oneor more pins may be used to penetrate into the substrate during themetal joining process. However, in other embodiments, the additivefriction stir tool has no pin capable of penetrating into the substrate.

Additional embodiments of additive friction stir tools according to theinvention can include a tool with a throat, where the filler materialand throat are operably configured to provide for continuous feeding ofthe filler material through the throat of the stirring tool. Inembodiments, the filler material is a powder, the throat of the tool isa hollow cylinder, and an auger shaped member disposed within the throatof the tool is used to force powder material through the throat of thetool onto the substrate. The filler material can be delivered by pullingor pushing the filler material through the throat of the stirring tool.

Additional embodiments can comprise an additive friction stir toolcomprising: a non-consumable body formed from material capable ofresisting deformation when subject to frictional heating and compressiveloading; a throat with an internal shape defining a passagewaylengthwise through the non-consumable body; an auger disposed within thetool throat with means for rotating the auger at a different velocitythan the tool and for pushing powdered filler material through the toolthroat; whereby the non-consumable body is operably configured forimposing frictional and adiabatic heating and compressive loading of thefiller material against a substrate resulting in plasticizing of thefiller material and substrate.

In embodiments, the tool and auger preferably rotate relative to thesubstrate. In further embodiments, the tool and auger rotate relative toone another, i.e., there is a difference in rotational velocity betweenthe auger and the tool body. There may be some relative rotation betweenthe filler material and the substrate, tool, or auger. The fillermaterial and tool are preferably not attached to one another to allowfor continuous or semi-continuous feeding or deposition of the fillermaterial through the throat of the tool.

For example, the filler material to be joined with the substrate may beapplied to the substrate surface using a “push” method, where arotating-plunging tool, e.g., auger, pushes the filler material throughthe rotating tool, such as a spindle. Feed material can be introduced tothe tool in various ways, including by providing an infinite amount offiller material into the tool body from a refillable container inoperable communication with the tool.

In embodiments, the filler material is a powdered solid and is fedthrough the tool body using an auger shaped plunging tool (e.g., athreaded member). In such an embodiment, the plunging tool may or maynot be designed to move or “plunge” in a direction toward the substrate.For example, the threaded configuration of the auger itself is capableof providing sufficient force on the powdered feed material to directthe filler material toward the substrate for deposition, without needingvertical movement of the auger relative to the tool.

As the spindle and plunging tool rotate, compressive loading andfrictional heating of the filler material can be performed by pressingthe filler material into the substrate surface with the downward force(force toward substrate) and rotating speed of the additive frictionstir tool.

During the metal joining process, it is preferred that the spindlerotate at a slightly slower rate than the auger. Alternatively, inembodiments, the spindle can also be caused to rotate faster than theauger. What is important in embodiments is that there is relativerotation between the spindle and the auger during application of thefiller material. Due to the difference in rotational velocities, thethreaded portion of the auger provides means for pushing the fillermaterial through the tool body to force the material out of the tooltoward the substrate. The threads impart a force on the feedstock thatpushes the feed material toward the substrate much like a linearactuator or pneumatic cylinder or other mechanical force pushing on asurface of the feedstock. Even further, it may be desired in someapplications to alter the rotational velocity of the tool body and/orauger during deposition of the filler material.

Deposition rate of the filler material on the substrate can be adjustedby varying parameters such as the difference in rotational velocitybetween the auger screw and the spindle, or modifying the pitch of thethreads on the auger. If desired, for particular applications it may bewarranted to control filler material temperature inside or outside ofthe tool body. Such thermally induced softening of the filler materialprovides means to increase the rate of application of the material.

In the context of this specification, the terms “filler material,”“consumable material,” “feed material,” “feedstock” and the like may beused interchangeably to refer to the material that is applied to thesubstrate from the additive friction fabrication tooling. In anembodiment, a powder filler material is used in combination with anauger disposed in the tool throat for applying a constant displacementto the filler material within the throat.

The filler material (for example, powder or solid feedstock) can be fedthrough the rotating spindle where frictional heating occurs at thefiller/substrate interface due to the rotational motion of the fillerand the downward force applied. The frictional and adiabatic heatingthat occurs at the interface acts to plasticize the substrate and fillermaterial at the interface resulting in a metallurgical bond between thesubstrate and filler.

A mechanism as shown in FIG. 3 was conceived to feed powder into thespindle and force it out of the spindle while ensuring the filler iskeyed into the spindle. This system utilizes an auger screw 17 to forcepowder through the spindle at a defined rate, which is one means capableof accomplishing this purpose. Additional methods of feeding solid stockkeyed into the orientation of the spindle and rotating at the exact rateof the spindle are conceivable. For example, force can be applied to thefiller material using a metal rolling mill type mechanism which isrotating with the spindle.

In such an embodiment, the spindle is spinning at a desired rotationalvelocity and the auger screw is driven at a different rotational speedin the same rotational direction which acts to force material out of thespindle. As shown in FIG. 3, the angular rotational speed or velocity ofthe friction stir tool is identified as ω1 and the angular rotationalvelocity of the auger is identified as ω2. In the context of thisspecification, the terms “rotational speed,” “rotational velocity,”“angular speed,” and “angular velocity” can be used interchangeably andrefer to the angular velocity of a component of the tool during use. Theauger screw can rotate at a slower speed than the spindle, or inpreferred embodiments the auger screw can rotate faster than thespindle. What is important is that there is relative rotation betweenthe spindle and auger to cause filler material to be forced through thethroat of the tool.

The pitch of the threaded auger screw and the volumetric pitch rate ofthe screw will affect the deposition rate under certain circumstances,and can be modified to accomplish particular goals. It is within theskill of the art to modify the pitch of the threads on the auger toobtain a certain desired result. The terms “tool,” “friction stir tool,”“spindle,” “tool body,” and the like as used in this specification maybe used to refer to the outer portion of the tool body, which comprisesa passageway lengthwise through the tool for holding and dispensing feedmaterial through the tool. This passageway, or throat, is generally theshape of a hollow cylinder. The hollow cylinder can be configured tohave a wider opening at the top of the tool for accommodating the augerand powder material and a smaller opening at the base of the tool wherethe feed material is dispensed from the tool. Thus, the shape of thethroat of the tool need not be consistent throughout the length of thetool throat and can be configured to converge from one lengthwise end ofthe tool to the other. As shown in FIG. 3, the throat of the tool cancomprise a first region which is the shape of a hollow cylinder of afirst diameter. This region can transition into a second region which isthe shape of a hollow cylinder of a second smaller diameter. Thetransition region can be a converging hollow cylinder or funnel shapedregion to allow the first and second region to be connected seamlessly.

Disposed within the tool body is an auger 17. In the context of thisspecification, the terms “auger,” “screw,” and “plunger” may be used torefer to a component of the tool that is disposed within the tool throatfor pushing or pulling material through the throat. Also within thisspecification, the auger can be considered a component of the frictionstir tool body. The auger can have the general shape of a screw withthreads, as shown in FIG. 3, or can be shaped in a spiral configurationsimilar to a spring. When disposed within the tool throat, there may beclearance between the auger 17 and the inside surface of the tool throatto allow for the passage of feed material between the auger and thethroat. The inside of the surface of the tool throat includes sleeve 19and bore 21. In other embodiments, there is only enough space to allowfor rotation of the auger without interference from the surface of thethroat. Preferably, the auger and tool body or spindle are not attachedto one another. Each is operably connected with means for rotating andtranslating the components relative to a substrate surface, such thatthe auger and tool can rotate at different speeds but translate relativeto the substrate at the same speed. It is preferred to keep the augerdisposed within the tool throat in a manner such that there is norelative translational movement between the auger and tool body.

Powdered materials can be fed into the top of the spindle using afluidized powder delivery system. Any type of powder delivery system canbe used in connection with the tools and systems of the presentinvention. For example, a gravity-fed powder feeder system can be used,such as a hopper. One such feed system is the Palmer P-Series VolumetricPowder Feeder from Palmer Manufacturing of Springfield Ohio, which iscapable of delivering feed material from 0.1-140 cu. ft. per hour, andwhich comprises a flexible polyurethane hopper, stainless steelmassaging paddles, 304 stainless steel feed tube and auger, 90-volt DCgearhead drive motor, flexible roller chain drive system, sealed drivetrain and cabinet, and solid state control and pushbutton controls. Thefeed system preferably comprises a reservoir for holding powder fillermaterial, a mixer for mixing powder(s) added to the reservoir, and apassageway for delivering feed material from the hopper to the throat ofthe tool body. As feed material is dispensed into and from the tool,more feed material is delivered into the tool from the hopper. In thismanner, the feed material is continuously or semi-continuouslydelivered. The gravity-fed dispensing systems allow for feed material toautomatically be dispensed from the hopper to the friction stir toolduring use as soon as material within the tool is dispensed.

In embodiments, a mix of powder types can be added to the hopper whichis operably connected with the stir tool. Alternatively, severaldifferent types of powder can be added individually to the hopper, thenmixed within the hopper and dispensed as a mixture to the friction stirtool during use. For example a metal powder and ceramic powder could befed into the spindle at the same time, from the same or separatehoppers, and upon consolidation/deposition the filler would be a metalmatrix composite (MMC). As used herein, the term “metal matrixcomposite” means a material having a continuous metallic phase havinganother discontinuous phase dispersed therein. The metal matrix maycomprise a pure metal, metal alloy or intermetallic. The discontinuousphase may comprise a ceramic such as a carbide, boride, nitride and/oroxide. Some examples of discontinuous ceramic phases include SiC, TiB₂and Al₂O₃. The discontinuous phase may also comprise an intermetallicsuch as various types of aluminides and the like. Titanium aluminidessuch as TiAl and nickel aluminides such as Ni₃Al may be provided as thediscontinuous phase. The metal matrix may typically comprise Al, Cu, Ni,Mg, Ti, Fe and the like.

EXAMPLE

FIG. 4 is a macrograph image showing a cross section of an article ofmanufacture comprising two different metals (molybdenum and copper) inan interlocking configuration prepared according to an embodiment of theinvention. The substrate comprises molybdenum and multiple grooves inthe surface of the substrate. The cross-sectional shape of the groovesin the substrate is rectangular. Copper was added to the surface of thesubstrate using an additive friction stir tool. At least one side of thegrooves was deformed during the additive friction stir process toprovide for a mechanical interlocking configuration between themolybdenum substrate and the copper coating. In the area of the jointbetween the molybdenum and copper, each of the copper and molybdenumhave two-dimensional projections into this area as shown. Some of thetwo-dimensional projections are of convex polygon shape and some are ofconcave polygon shape. Other combinations of materials can also be used,including the same material as both the substrate and the coating.Additionally, the following combinations, W—Cu, Ta—Cu, Ti—Al, Fe(steel-Al), Al—Cu, Fe—Mg, Ti—Mg, and Al—Mg, are also possible forexample for different substrate and coating material.

The present invention has been described with reference to particularembodiments having various features. In light of the disclosure providedabove, it will be apparent to those skilled in the art that variousmodifications and variations can be made in the practice of the presentinvention without departing from the scope or spirit of the invention.One skilled in the art will recognize that the disclosed features may beused singularly, in any combination, or omitted based on therequirements and specifications of a given application or design. Whenan embodiment refers to “comprising” certain features, it is to beunderstood that the embodiments can alternatively “consist of” or“consist essentially of” any one or more of the features. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention.

It is noted in particular that where a range of values is provided inthis specification, each value between the upper and lower limits ofthat range is also specifically disclosed. The upper and lower limits ofthese smaller ranges may independently be included or excluded in therange as well. The singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is intendedthat the specification and examples be considered as exemplary in natureand that variations that do not depart from the essence of the inventionfall within the scope of the invention. Further, all of the referencescited in this disclosure are each individually incorporated by referenceherein in their entireties and as such are intended to provide anefficient way of supplementing the enabling disclosure of this inventionas well as provide background detailing the level of ordinary skill inthe art.

1. An article of manufacture comprising: two metals joined in aninterlocking configuration; and a joint between the two metals along anarea of interlocking; wherein a cross section of the joint reveals eachof the two metals providing a plurality of two-dimensional projectionsinto the area of interlocking; wherein at least one of thetwo-dimensional projections has a base and two sidewalls and thesidewalls are asymmetric to one another.
 2. The article of manufactureof claim 1, wherein the two metals are different from one another. 3.The article of manufacture of claim 1, wherein at least one of thetwo-dimensional projections has one sidewall which is curvilinear. 4.The article of manufacture of claim 1, wherein the sidewalls have ageometry that varies along the length of the joint.
 5. The article ofmanufacture of claim 1, wherein at least one of the two-dimensionalprojections is concave polygon-shaped.
 6. The article of manufacture ofclaim 1, wherein the cross-section of the joint reveals that theplurality of two-dimensional projections is arranged in a row.
 7. Thearticle of manufacture of claim 6, wherein the two metals are differentfrom one another and the plurality of two-dimensional projectionsalternate between a first metal adjacent to a second metal.
 8. Thearticle of manufacture of claim 1, wherein the two metals are eachindependently chosen from steel, Al, Ni, Cr, Cu, Co, Au, Ag, Mg, Cd, Pb,Pt, Ti, Zn, Fe, Nb, Ta, Mo, W, or an alloy or composite comprising oneor more of these metals.
 9. The article of manufacture of claim 2,wherein the two metals are each independently chosen from steel, Al, Ni,Cr, Cu, Co, Au, Ag, Mg, Cd, Pb, Pt, Ti, Zn, Fe, Nb, Ta, Mo, W, or analloy comprising one or more of these metals.
 10. The article ofmanufacture of claim 1, which is a structural component of anautomobile, a ship, a tank, a plane, or an aerospace vehicle.
 11. Thearticle of manufacture of claim 1, wherein the cross section of thejoint reveals a metallurgical bond between the two metals.
 12. Anarticle of manufacture comprising: a substrate with a surface comprisinga plurality of grooves; a layer of material joined to the substratealong a joint; wherein the layer of material joined to the substrate hasat least one two-dimensional projection extending into at least one ofthe plurality of grooves; wherein the at least one two-dimensionalprojection and the at least one groove are provided in an interlockingconfiguration; wherein each the at least one two-dimensional projectioncompletely fills the at least one groove.
 13. The article of manufactureof claim 12, wherein a cross-section of the joint reveals that at leastone of the two-dimensional projections is concave polygon-shaped. 14.The article of manufacture of claim 12, wherein a cross-section of thejoint reveals that at least one of the two-dimensional projections hasone sidewall which is curvilinear.
 15. The article of manufacture ofclaim 12, wherein sidewall geometry of the at least one groove variesalong the length of the joint.
 16. The article of manufacture of claim12, wherein a cross-section of the joint reveals that at least one ofthe two-dimensional projections has two sidewalls which are asymmetricto one another.
 17. The article of manufacture of claim 12, wherein thesubstrate and the layer of material joined to the substrate comprisematerials each independently chosen from metals, metallic materials,metal matrix composites (MMCs), polymers, polymeric materials, ceramics,ceramic materials, steel, Al, Ni, Cr, Cu, Co, Au, Ag, Mg, Cd, Pb, Pt,Ti, Zn, Fe, Nb, Ta, Mo, W, or an alloy comprising one or more of thesemetals, as well as combinations of any of these materials.
 18. Thearticle of manufacture of claim 12, wherein the substrate and the layerof material joined to the substrate are each a metal matrix compositecomprising a metal matrix and a ceramic phase, wherein the metal matrixcomprises one or more of a metal, a metal alloy, or an intermetallic andthe ceramic phase comprises a ceramic.
 19. The article of manufacture ofclaim 12, wherein the substrate and the layer of material joined to thesubstrate comprise different materials.
 20. An article of manufacturecomprising: a first and second metal joined together along a region ofinterlocking; wherein a cross section of the region of interlockingreveals a plurality of two-dimensional projections of the first metaland a plurality of two-dimensional projections of the second metal;wherein the plurality of two-dimensional projections comprise sidewallswith varying geometry.
 21. The article of manufacture of claim 1,wherein the two metals are the same metal.
 22. The article ofmanufacture of claim 1, wherein the two-dimensional projections havelinear sidewalls.
 23. The article of manufacture of claim 6, wherein thetwo metals are the same metal and the plurality of two-dimensionalprojections alternate between a first metal adjacent to a second metal.24. The article of manufacture of claim 1, wherein the cross section ofthe joint reveals a metallurgical bond between the two metals along theentire joint.
 25. An article of manufacture comprising: two metalsjoined in an interlocking configuration; and a joint between the twometals along an area of interlocking; wherein the joint comprises apartial mechanical and metallurgical joint between the two metals;wherein a cross section of the joint reveals each of the two metalsproviding a plurality of two-dimensional projections into the area ofinterlocking; and wherein at least one of the two-dimensionalprojections has a base and two sidewalls and the sidewalls are symmetricto one another.
 26. The article of manufacture of claim 1, wherein theplurality of two-dimensional projections are arranged in any pattern.27. The article of manufacture of claim 26, wherein the plurality oftwo-dimensional projections are arranged non-linearly.
 28. The articleof manufacture of claim 12, wherein the two-dimensional projections arelinear.
 29. The article of manufacture of claim 12, wherein across-section of the joint reveals that at least one of thetwo-dimensional projections has two sidewalls which are symmetric to oneanother.
 30. The article of manufacture of claim 1, wherein the twometals are each independently chosen from metals, metallic materials,metal matrix composites (MMCs), steel, Al, Ni, Cr, Cu, Co, Au, Ag, Mg,Cd, Pb, Pt, Ti, Zn, Fe, Nb, Ta, Mo, W, or an alloy comprising one ormore of these metals, as well as combinations of any of these materials.